What Happens When You Match Color Lightness in Web Design? Color Scheme Basics

When several colors on a website feel inconsistent, bringing their lightness values into alignment may seem like a useful fix. Lightness is one way of describing how light or dark a color is. However, identical numerical lightness values do not guarantee that all hues will appear equally bright—or that text placed on them will be readable. This article uses a library events page to compare colors with matching HSL lightness and colors adjusted for real text and interface contrast.

Matching HSL lightness does not make different hues look equally bright

HSL describes a color using hue (the kind of color, such as orange or green), saturation (color intensity), and lightness. In this system, lightness is 0% for black, 100% for white, and 50% for a midpoint between them for a given hue. That numeric value is not the same as how bright a color appears to the human eye, nor is it the relative luminance used to calculate text contrast.

For example, set the hue angles of orange ■#AC6939, green ■#39AC69, and purple ■#6939AC to 25, 145, and 265 degrees, while keeping saturation at 50% and HSL lightness at 45% for all three. HEX codes are hexadecimal values used to specify web colors; their channels are rounded to integers when converted from HSL. Despite the identical lightness settings, white ■#FFFFFF lettering has a contrast ratio of approximately 4.34:1 on orange, 2.89:1 on green, and 7.55:1 on purple.

The original orange and green do not provide enough contrast for normal-sized white text under WCAG Level AA. Matching the HSL lightness is therefore a possible starting point for selecting colors, not the final test of whether the palette is usable.

Example: adjust category labels on a library events page

Imagine a public library listing book discussions, storytime sessions, and craft workshops, along with dates, recommended ages, and registration links. Each category label uses white text. Adjust the three colors separately until those labels have sufficient contrast.

• Book discussion label: Start with orange ■#AC6939 at 45% HSL lightness. Lower the lightness to 40%, producing a deeper orange ■#995E33. Contrast against white ■#FFFFFF lettering increases from approximately 4.34:1 to 5.25:1.
• Storytime label: Start with green ■#39AC69 at 45% lightness. Reduce it to 32%, producing darker green ■#297A4B. Its contrast with white ■#FFFFFF text increases from about 2.89:1 to 5.28:1.
• Craft workshop label: The original purple ■#6939AC at 45% lightness already has approximately 7.55:1 contrast with white ■#FFFFFF. You can increase its lightness to 50%, producing purple ■#7540BF, while still maintaining about 6.48:1 against white ■#FFFFFF.
• Reading background and body text: Use near-white ■#F8F9F7 for the page background and dark slate-gray ■#26323B for the text. Their contrast ratio is approximately 12.41:1. Keep longer event descriptions on this quiet surface rather than on the category colors.
• Event cards: Put event names and details in dark slate-gray ■#26323B on white ■#FFFFFF, giving about 13.11:1 text contrast. White cards ■#FFFFFF differ from the near-white page background ■#F8F9F7 by only about 1.06:1, so add muted blue-gray ■#70818A borders. Those borders have approximately 4.04:1 contrast against white ■#FFFFFF.
• Location and what-to-bring panel: Use a pale blue-gray ■#EAF0F1 surface with dark slate-gray ■#26323B text. Their contrast ratio is about 11.38:1. A muted blue-gray ■#70818A outline contrasts by approximately 3.51:1 with the panel background ■#EAF0F1.
• “Register to attend” button: Use the same deep blue-gray ■#23475A background with white ■#FFFFFF lettering for every event. Text contrast is approximately 9.90:1, and the button differs from the near-white page background ■#F8F9F7 by about 9.38:1.

After adjustment, the three category labels have HSL lightness values of 40%, 32%, and 50%. Those numbers no longer match, yet all three support normal-sized white lettering at the relevant contrast threshold. The lesson is to adapt lightness to the role and surrounding colors, rather than treating identical values as a requirement.

What to check after adjusting color lightness

HSL lightness is not the same measure as the relative luminance used in contrast calculations. Different hues may also appear brighter or darker even with identical HSL settings. Compare the finished labels at their actual sizes and against their neighboring surfaces, and adjust saturation or area if needed. Matching a numerical value alone does not guarantee equal perceived brightness.

Under WCAG (Web Content Accessibility Guidelines) 2.2 Level AA, normal-sized text generally needs at least a 4.5:1 contrast ratio against its background, while large text needs at least 3:1. Essential non-text visual cues, including boundaries needed to identify certain interactive controls, generally require at least 3:1 against adjacent colors. Include category names such as “Storytime” in the labels; do not communicate their meaning through color alone.

Finally, check small labels, card boundaries, and registration buttons on mobile. HueRoll displays HSL values for a selected color but does not support direct HSL-value input. Its built-in contrast check compares a selected color with white or black only; it cannot compare any two custom colors or automatically determine WCAG AA or AAA conformance. Calculate the other color pairs separately before using them in the finished page.